Demodulated chrominance signal filter using impedance mismatched sections

Abstract

A filter network suitable for translating a signal such as a demodulated "I" chrominance component of a composite color television signal is disclosed. The filter network comprises first and second cascaded sections with mutually grossly mismatched terminating impedances, and are passively interconnected via a resistance of a value which substantially precludes interaction between the sections over a given range of frequencies within the passband of the signals being translated. Both sections are separately excited with signals to be translated. The first section provides wideband filtering and a large amount of delay relative to that provided by the second section. The second section provides signal amplitude peaking within a given portion of the frequency passband of the first section.

What is claimed is: 
     
       1. In a video signal processing system including a signal path for conveying video signals, frequency selective apparatus coupled to said signal path for translating signals conveyed by said signal path, comprising: a first frequency selective section including parameters determinative of the frequency response of said first section;   a second frequency selective section including parameters determinative of the frequency response of said second section;   resistance means for passively connecting said first section to said second section, said resistance means being of a value to substantially preclude mutual interaction between the parameters of said first and second sections over a given range of signal frequencies within the passband of signals to be translated; and   means for exciting said first and second sections with signals from said signal path to modify the amplitude-versus-frequency response of signals conveyed by said signal path, in accordance with the amplitude-versus-frequency responses of said first and second sections.   
     
     
       2. In a video signal processing system including a signal path for conveying video signals, frequency selective apparatus coupled to said signal path for translating signals conveyed by said signal path, comprising: a first frequency selective section;   a second frequency selective section;   resistance means for passively connecting said first section to said second section, said resistance means exhibiting a value substantially greater than the resistance value associated with said second section; and   means for exciting said first and second sections with signals from said signal path to modify the amplitude-versus-frequency response of signals conveyed by said signal path, in accordance with the amplitude-versus-frequency responses of said first and second sections.   
     
     
       3. Apparatus according to claim 2, wherein said second section is directly excited with signals to be translated, as derived from said signal path, at a point intermediate to said first and second sections.   
     
     
       4. Apparatus according to claim 2, wherein a first resistor terminates one end of said second section; and   said resistance means includes a second resistor for passively connecting said first section to said second section, said second resistor exhibiting a resistance value substantially greater than the combined resistance values of said first resistor and said second section.   
     
     
       5. Apparatus according to claim 4, wherein a third resistor terminates one end of said first section remote from the connection of said second resistor to said first section;   said second and third resistors exhibit substantially equal values; and   said second resistor exhibits a value substantially greater than the value of said first resistor.   
     
     
       6. Apparatus according to claim 2, wherein said first section provides signal filtering over a given frequency range and exhibits a given signal delay; and   said second section exhibits a peaked amplitude response within a given portion of said frequency range.   
     
     
       7. Apparatus according to claim 6, wherein said first frequency selective section comprises a high order low pass filter; and   said second frequency selective section comprises a single-tuned resonant circuit.   
     
     
       8. Apparatus according to claim 2, wherein said first and second sections comprise a direct current path from said signal path to a point of reference potential.   
     
     
       9. Apparatus according to claim 2, wherein said frequency selective apparatus including said first and second sections comprises a high order filter of the type having three terminals and two signal ports, and exhibiting a combined transfer function between said two signal ports corresponding to the combined transfer functions of said first and second sections; and   said filter is coupled via a single interface terminal to said signal path to effect filtering of signals conveyed by said signal path in accordance with said transfer function.   
     
     
       10. Apparatus according to claim 9, further comprising: means coupled to said filter for synthesizing, at said single interface terminal, an impedance related to the transfer function of said filter.   
     
     
       11. Apparatus according to claim 2, wherein said frequency selective apparatus comprises a signal filter, including said first and second sections, of the type comprising a first terminal corresponding to a signal port, a second terminal corresponding to a signal port, and a third terminal intermediate to said first and second terminals; said filter exhibiting a transfer function between said first and second terminals;   first means for coupling signals from said signal path to said first filter terminal;   second means for coupling said second filter terminal to a reference potential; and   third means for coupling signals from said signal path to said intermediate third terminal.   
     
     
       12. Apparatus according to claim 11, wherein said first and third coupling means include respective signal voltage sources for separately exciting said first and third filter terminals.   
     
     
       13. Apparatus according to claim 12, wherein a resistance couples a signal voltage to said first filter terminal; and   signal voltages applied to said resistance and to said third filter terminal exhibit similar phase and substantially equal magnitude.   
     
     
       14. In a video signal processing system including a signal path for conveying video signals, frequency selective apparatus for translating signals conveyed by said signal path, comprising: a first frequency selective section having first and second end portions;   a first resistor for terminating said first end portion of said first section;   a second frequency selective section having first and second end portions;   a second resistor for terminating said first end portion of said second section;   means, comprising a third resistor, for passively coupling together said second end portions of said first and second sections, said passive coupling means exhibiting a resistance value substantially greater than the combined resistance values of said second resistor and said second section; and   means for separately exciting said first and second sections directly with signals to be translated as derived from said signal path.   
     
     
       15. Apparatus according to claim 14, wherein said frequency selective apparatus including said first and second sections comprises a filter of the type having three terminals and two signal ports, and exhibiting a combined transfer function between said two signal ports corresponding to the combined transfer functions of said first and second sections;   said first signal port corresponds to said first terminal and is coupled to said first terminating resistor;   said second signal port corresponds to said second terminal and is coupled to said second terminating resistor;   said third terminal is coupled intermediate to said first and second terminals and is coupled to said first and second sections;   said first terminal is excited with signals to be translated as derived from said signal path;   said second terminal is coupled to a reference potential via said second resistor; and   said intermediate third terminal is excited with signals to be translated as derived from said signal path.   
     
     
       16. Apparatus according to claim 14, wherein said first and third resistors exhibit substantially equal values; and   said second and third resistors exhibit substantially different values.   
     
     
       17. In a system for processing a color television signal including a chrominance information component exhibiting a first amplitude level over a first frequency range and a second amplitude level lower than said first amplitude level over a second frequency range, frequency selective apparatus for processing said chrominance component, comprising: a first frequency selective section for providing signal filtering over said first and second frequency ranges, and exhibiting a given signal delay; and   a second frequency selective section exhibiting a peaked amplitude response encompassing frequencies within said second frequency range;   resistance means for passively connecting said first section to said second section, said resistance means being of a value substantially greater than the resistance value associated with said second section; and   means for exciting said first and second sections with signals from said signal path to modify the amplitude-versus-frequency response of signals conveyed by said signal path, in accordance with the amplitude-versus-frequency response of said first and second sections.   
     
     
       18. Apparatus according to claim 17, wherein said processing system comprises a color television receiver including: means for receiving a composite color television signal including a chrominance subcarrier signal containing chrominance modulation information in double sideband form over said first frequency range, and chrominance modulation information in single sideband form over a higher frequency range corresponding to said second frequency range;   means for synchronously detecting said modulated chrominance component to produce said chrominance information component having said first and second amplitude levels over said first and second frequency ranges; and wherein   said frequency selective apparatus filters output signals from said synchronous detecting means.   
     
     
       19. Apparatus according to claim 17, wherein said first frequency selective section comprises a high order low pass filter;   said second frequency selective section comprises a resonant circuit;   a first resistor terminates one end of said first section;   a second resistor terminates one end of said second section; and   said resistance means corresponds to a third resistor coupled to the other ends of said first and second sections for passively interconnecting said first and second sections in cascade, said third resistor exhibiting a resistance value substantially greater than the combined resistance values of said second section and said second resistor.   
     
     
       20. Apparatus according to claim 19, wherein said first and third resistors exhibit substantially equal values; and   said second and third resistors exhibit substantially different values.   
     
     
       21. In a signal processing system including a signal path for conveying signals to be translated, said signal path including an amplifier device for receiving input signals to be translated; frequency selective apparatus comprising: a first frequency selective section;   a second frequency selective section;   resistance means for passively connecting said first section to said second section, said resistance means exhibiting a resistance value substantially greater than the resistance value associated with said second section;   means for coupling said frequency selective apparatus including said first and second sections in series with a main current conduction path of said amplifier device;   means for exciting said first and second sections with signals from said signal path; and wherein   said frequency selective apparatus provides a direct current path for currents conducted by said main conduction path of said amplifier device.   
     
     
       22. Apparatus according to claim 21, and further comprising: a load resistance included in an output circuit of said amplifier device;   plural resistances, including said resistance means, for respectively terminating said first and second sections; and wherein   the DC gain of said amplifier device is primarily determined by the ratio of the value of said load resistance to the combined values of said plural terminating resistances.   
     
     
       23. Apparatus according to claim 22, wherein said amplifier device comprises a transistor with a base input electrode, a collector electrode coupled to said load resistance, and an emitter electrode coupled to said frequency selective apparatus.